Because any geometrical inductor (a coil being the standard textbook
example) also necessarily possesses a parasitic self-capacitance
which starts to dominate at high frequencies, its non-dissipative
impedance is limited by the vacuum impedance,
\(\sim \sqrt{\mu _0/\epsilon _0}=4\alpha R_Q\) , where
\(\alpha \approx {1}/137\)  is the fine structure constant, and
\(R_Q\approx 13\:\mathrm {k}\Omega \)  is the resistance
quantum [1]}.
Indeed, the inductance of a geometrical inductor is due to the
magnetic field produced by the current, which acts on the current
itself. The relativistic nature of this effect is the intrinsic
reason for its weakness.
This limitation can be overcome by using superconducting
materials whose inductance is due to the kinetic energy of the Cooper
pair condensate [2]}, and thus is of non-relativistic
origin. The term “superinductance” is often used to denote such
superconductivity-based inductance.
